1. Field of the Invention
This invention relates to a pneumatic-hydraulic brake booster or air over hydraulic brake booster for a vehicle.
2. Brief Description of the Prior Art
In a conventional pneumatic-hydraulic brake booster, an internal space of a cylindrical casing is divided to two chambers by a power piston which is slidably fitted to the cylindrical casing. In operation, compressed air is supplied to the one chamber. An output rod is fixed to the power piston, and it extends across the other chamber into a hydraulic cylinder body of a master cylinder part.
The compressed air is supplied to the one chamber directly from a brake valve or through a relay valve from the brake valve. In the former case, only one conduit is connected between the brake booster and the brake valve. The brake system is simple. However, in the latter case, one conduit is connected between the brake valve and the relay valve fixed to a part of the chassis of the vehicle, and another conduit should be connected between the relay valve and the brake booster. The brake system is so complicated. More parts are necessary. Manufacturing efficiency or productivity is low.
When the distance between the brake valve and the brake booster is long, the braking operation retards behind the tread of the brake pedal in the booster without relay valve. The retard can be reduced with the relay valve arranged near the brake booster. However, the conventional brake booster has the above described defects.